Electric machines such as motors and generators are known to suffer from eddy current losses generally due to the fact that eddy currents are generated in the pole face of rotors. This occurs by reason of high frequency fluxes in the air gap between rotors and stators. While the losses depend on the frequencies generated and materials utilized for rotor fabrication, they can be very high, particularly in high speed electric machines, which reduces operating efficiency considerably.
Generally, it is recognized that eddy current loss=V.sup.2 /R, where V is voltage induced in the surface of the rotor and R is the resistance to eddy current. In order to reduce losses caused by eddy currents induced by fluxes in the air gap between rotors and stators, laminated rotors consisting of alternating layers of conductive material and insulation are conventionally utilized since the insulation layers break up eddy currents and, therefore, tend to reduce eddy current loss. Unfortunately, it is impractical to use laminated rotors with high speed and large rotor diameter electric machines, i.e., electric machines operating in excess of 40,000 RPM with 3.5 inch rotor diameter.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objective by providing an electric machine and method of improving efficiency of electric machines.